Telephone system



Aug, 112 1924. 1,504,294

S. B. WILLIAMS, JR. ET AL TELEPHONE SYSTEM 'Filed Sent. 24. 1920 5 Sheets-Sheet 1 o o o o O O (D g} G O O O 0 O G 10 O :O O

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5. B. WILLIAMSQJR, ET AL TELEPHONE SYSTEM Filed Sept. 24. 1920 5 Sheets-Sheet 5 Samuel 5. mm/m \lw:

Patented Aug. I2, 192% SAMUEL 1B. WILLIAMS, JR, OFBROOKLYN, AND EIDVTARD E. HINRICHSEN, OF NEW YORK, N. Y., ASSIGNORS T'O WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE SYSTEM.

Application filed September 24, 1920. Serial No. 412,482.

To all whom it may concern:

Be it known that we, SAMUEL B. WIL- LIAMS, Jr, and EDWARD E. HINRICHSEN, citizens of the United States, residing at Brooklyn, in the county of Kings and State of New York, and. at New York, in the county of New York and State of New York, respectively, have invented certain new and useful Improvements in Telephone Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to improvements in telephone systems and has particular reference to private branch exchange systems which may be used in conjunction with either manual or machine switching central otfices.

Its object is to provide a system of this type which shall be simple and efficient in operation and cheap to manufacture.

A feature of the invention is the provision of a switch which is responsive to impulses and which contains novel means for preventing under certain conditions, any further operation of the switch should additional impulses be inadvertently transmitted.

Another feature is the provision of a simple and efiicient stepping circuit for the switch which will permit of an automatic trunk hunting operation. In accordance with this object, a stepping relay is provided, the original energizing circuit for which is controlled through a brush of the switch and which is normally short-circuited by an impulse responsive relay. Following the first stepof the switch, the corn trol of the stepping circuit is removed from said brush and is returned thereto during any trunk hunting operation.

A further feature is a novel arrangement of the stepping circuit whereby the switch is caused to take a full step for each interruption of the circuit controlled by the line relay, independent of the duration of such interruption.

A still further feature is the provision of means operable, upon the extension of calls from subscribers within the private branch exchange to a central office over a trunk,

to discriminate between the character of such calls and to signal the attendant at the private branch should certain calls require supervlsion.

Other features will appear in the course of the following description when taken in connection with. the accompanying drawings, wherein. Fig. 1 shows the calling line and the switch individual thereto; Fig. 2 shows the P. B. X. attendants circuit; Fig. 3 shows the trunk circuit; Fig. 4c shows a switch associated with the trunk by means of which the attendant may connect the trunk with any of the P. B. X. stations;

Fig. 5 shows a code switch by. means of which the P. B. X. attendant is signaled when the calllng party dials certain numbers; and Fig. 6 shows the manner in which Figs. 1 to 5, inclusive should beassembled.

Briefly stated, the invention provides a private branch exchange in which the subscribers are assigned individual switches having access to other subscribers lines; and attendants and central office trunks. In the bank of each switch the terminals of the lines and trunks are interspersed and arranged in groups, i one group of sub scribers" lines being disposed between the attendants and central office trunks. Provision is made in the switch circuit whereby the switch will automatically seek an idle trunk'when the terminals of busy trunks are engaged by the brushes thereof. A subscriber may establish connection to the attendants position or may secure. direct connection with the central oflice.

When anincoming call has been answered by the subscriber the apparatus is automati cally restored to normal upon the hanging up of the subscribers receiver and the disconnection of the trunk line at the central oflice, without any action on the part of the private branch exchange attendant. The subscriber may however signal the attendant if desired, as for instance if he wishes her to transfer the call toanother station,

The attendant may originate a call to the central office and then if desired extend it to a station in the same manner as were an incoming call.

The trunks leading to the central office may terminate in a manual exchange or in a machine switching office and, in the latter instance, provision is made whereby the attendant may have supervision over'certain connections, such as when a toll call is initiated. For this purpose, use is preferably made of a code switch and circuit, shown in Fig. 5, which, upon the seizure of a central oflice trunk by a calling subscriber, establishes a condition whereby, when impulses are transmitted by said subscriber, the same will operate the code switch and be simultaneously repeated at the central oflice to ac tuate the switches thereat. The code switch, in this operation, discriminates between the character of calls initiated by subscribers by setting up certain conditions in the circuit therefor in response to the impulses transmitted. If a call is such as to require supervision by the attendant, discriminating relays in the code circuit operate in response to the dialing operations, to effect a condition whereby a signal before the attendants position individual to the seized trunk will be operated. On the other hand, if the call does not require supervision, the code switch will nevertheless operate, but the discriminating relays will fail to establish the condition which causes the actuation of the signal before the attendants position.

Incoming calls from the central office are routed through theattendant who may complete a connection to a subscriber by means of a switch individual to the trunk taken for use.

The attendant is also provided with an individual switch (Fig. 2) which is employed when the attendant desires to establish connection to a subscriber independent of a central oflice trunk.

It is believed that the invention will now be fully understood from the following description of the various operations.

Local, calls.

.101, the inner left-hand back contact and armature of cut-off relay 102, the apparatus at substation A, the outer left-hand armature and back contact of relay 102, the inner right-hand armature and back contact of relay 101, and the left-hand winding of relay to ground. The energization of relay 100 establishes a circuit for slow-to-release relay 103, extending from grounded battery through the winding of said relay, the lefthand contact and armature of relay 100, and the left-hand armature and contact of relay 104 to ground. Relay 103 energizes and in so doing opens, through its outer normal contact and armature, the energizing circuit for cut-01f relay 102, and thus prevents energization of this relay while the subscriber at substation A is calling. The energization of relay 103 also applies a busy potential to the multiple test terminal 105 of the calling line by extending ground to this terminal through the outer armature and front contact of relay 103, the inner right-hand normal contact of relay 1.04:, and the inner left hand normal contact of relay 106. The operation of relay 103 also closes a circuit for the stepping relay 107, extending from ground through the alternate contact and inner armature of relay 103, the left-hand back contact and armature of relay 101, the right-hand normal contact of slow-to-release relay 108, brush 109 and its associated normal terminal, left-hand winding of relay 107, and the resistance 110 to grounded battery. Relay 107, however, does not operate at this time due to a shunt circuit extending from grounded battery through the resistance 110, the' outer left-hand back con tact and armature of relay 106, the righthand contact of relay 100, and from thence to ground at relay 103 over the previously traced circuit.

The switch is now in condition to receive impulses transmitted from the calling substation, and in response to the operation of the impulse sender the circuit for relay 100 is interrupted to cause this relay to retract its armatures. Upon the first deencrgization of relay 100 the shunt circuit for the stepping relay 107 is opened and this relay energizes over the circuit described therefor through brush 109. The energization of relay 107 establishes a circuit for the motor magnet 111, extending from grounded battery through the resistance 112, the winding of the motor magnet, and the inner front contact and left-hand armature of relay 107 to ground. The motor magnet operates to step the brushes of the switch from their normal positions on to the first set of active terminals of the switch bank. The energization of relay 107 also closes an obvious circuit for the slowtorelease relay 108, which maintains its armatures attracted during the transmission of the series of impulses. In the operation of the motor magnet 111 the contact thereof does not open until the magnet has nearly completed its stroke, and therefore upon the energization of relay 107 a locking circuit is established for this relay extending through its winding, right-hand front contact and armature, the contact of magnet 111, and from thence to ground through the left-hand armature of relay 107. This locking circuit will maintain relay 107 operated a suflicient time to permit the full operation of the motor magnet even though relay 100 is again operated, in the meanwhile, to establish a shunt circuit for relay 107. After the motor magnet has completed its first operation and relay 100 is again energized previous to the second interruption of the circuit therefor by the impulse sender, the previously mentioned shunt circuit is again established and relay 107 releases. The energizing circuit forthis relay now extends, through its left-hand winding, the outer alternate contact of relay, 108, and from thence to ground through the left-hand normal contact of relay 101 and the inner alternate contact of relay 103. lVhen relay 108 is operated in response to the first energization of relay 107, the ground on brush 109, extending from the alternate contact and inner armature of relay 103, is removed from said brush and a circuit is established for relay 113, extending from grounded battery through the resistance 112, the lefthand winding of relay 113, the inner alternate contact and armature of relay 108, resistance 114, the inner normal contact of relay 104, and the left-hand. armature and front contact of relay 103 to ground. Relay 113 energizes in this circuit and disconnects brushes 115, 116, 117, and 118 from their associated circuits. It will thus be seen that in response to three impulses, the line of substation B being connected to the fourth set of terminals in the bank of the switch, the brushes of the switch will he stepped to said set of terminals, and upon the return of the dial at substation A to normal, relay 100 will remain energized. This will cause the release of relay 107 to open the energizing circuit for relay 108, which, after an interval, releases. With the brushes on the fourth set of terminals'and relay 108 in its normal position, it will be obvious that the energizing circuit for stepping relay 107, through the right-hand alternate contacts of relay 108, will be permanently opened and the stepping relay will be prevented from energizing should any further impulses be sent, or should the switchhook at substation A be accidentally depressed.

Should substation B be busy, a ground will be found upon the test terminal thereof associated with brush 117, and this ground will be extended through the outer left-hand armature and front contact of relay 113, the middle left-hand armature, normal contact, and left-hand winding of test relay 106, the inner normal contact of relay 108, the left hand winding of relay 113, and the resistance 112 to grounded battery. This circuit causes the energization f relay 106 to series with relay 113 and prevents the release of the latter relay. Relay 106, in energizing,

&

disconnects itself from brush 117 and locks up through its left-hand alternate contact, the normal contact of relay 104, and the left-hand armature and front contact of relay 103 to ground. It will be obvious that relay 113 will remain energized through that portion of the locking circuit just described for relay 106. A busy tone will now be applied to the calling line from ground through the secondary winding of the busy tone apparatus BZ, the back contact and outer right armature of relay 104:, the righthand armature and back contact of relay 102, and the front contact and outer right-hand armature of relay 113 to the lower side of the calling line. The subscriber at substation A, upon hearing this busy tone, replaces his receiver upon its switch-hook, thereby opening the energizing circuit for relay 100, which then releases. The restoration of relay 100 to normal opens the energizing circuit for relay 103 which, after an interval, releases. The release of relay 103 opens the locking circuit for relays 106 and 113, and the latter thereupon restore to normal. Also, upon the release of relay 103, ground is extended through the alternate contact of said relay and the back contact and middle right armature of relay 104 to the brush 119, which is now in engagement with the continuous segment with which it is associated. This ground is extended through the right-hand windings of relays 106 and 113 and the left-hand winding of relay 101 to energize these'relays in parallel. The ground on the brush 119 is extended through the right-hand armature and contact of relay 106, the back contact and righthand armature of relay 107, the armature,v contact and winding of motor magnet 111 and the resistance 112 to grounded battery. The energization of relay 101 disconnects line relay 100 from the calling line while the switch is being restored to normal, and the energization of relay 113 again disconnects brushes 115, 116, 117 and 118 from their associated circuits. The motor magnet 111 operates in the self-interrupting circuit just described for the same and steps the brushes of the switch toward their normal positions as long as the brush 119 is in engagement with the off-normal segment associated therewith. When the brushes reach their normal positions the circuit for the motor magnet is permanently opened and the switch comes to rest and is in position to receive another call.

Assuming now that the called substation l? is idle, the terminal with which the test brush 1.17 is in engagement will be free from ground and relay 106 will not operate. Also no holding circuit will be established for relay 113 and this relay will thereupon deenergize. The closure of the right-hand back contacts of relay 113 extends the call- &

ing line through the condensers 120 and 121 to the brushes 115 and 116 which are now in engagement with the terminals of the called line. Ground is also extended, by the release of relay 113, to the brush 117 from the front contact and left-hand armature of relay 103, the normal contact of relay 10 1, the back contact and outer left-hand armature of relay 113 to cause the multiple contacts of the called line to test busy should other switches engage the terminals of said line. The grounding of the brush 117 operates the cut-01f relay 102 of the called line over a circuit extending from grounded battery through the winding of relay 102, the back contact and armature of relay 103, the normal contact of relay 10 1, and the normal contact f relay 106 to the brush 117. Relay 102 energizes and in so doing connects the source of ringing current 122 through the left-hand winding of relay 10 1 to the apparatus at substation B to operate the ringer thereat. Due to the resistance of the apparatus at substation B, suflicient current does not flow through the left-hand winding of relay 101' to energize the same until the subscriber at said substation removes his receiver from the switchhook., whereupon relay 104; energizes and in so doing opens the energizing circuit for relay 102', which then releases. The calling line is thereupon connected through the back contacts of relay 102 to the called substation and conversation may now proceed between the subscribers. In energizing, relay 1041' establishes a locking circuit for itself extending from grounded battery through its right-hand winding, armature .and alternate contact, and from thence over the energizing circuit for the cut-off relay 102. Relay 100 also energizes when the calling and called lines are interconnected to supply talking current to the called line but the operation of said relay has no other effect at this time inasmuchas relay 104 is energized. At the termination of the con versation between the subscribers, the replacing of the receiver upon its switchhook at substation A causes the release of the switch in the same manner as previously described. If the called line is located in the second group of subscribers lines, two series of im pulses are required. to be transmitted. The lines in this group may be numbered from 93 to 99, inclusive. The first series of nine impulses steps the switch, as before, until the tenth set of terminals in the switch bank is reached. Brush 109 will then be resting upon terminal 123, this being shown as the fifth terminal as certain of those allotted to lines in the first group are omitted. When engaged with terminal 123, brush 109 is connected to the left-hand winding of stepping relay 107 and upon the impulses of the second series being transmitted, relay 107 operates with the same result as described in connection with stepping of the switch from its normal position. The remaining operation is also as previously set forth.

UaZZs to P. B. X. attendant.

position and it is to be noted that only the terminal associated with the first trunk, and over which brush 109 passes, is connected to the left-hand winding of the stepping relay 107 for a purpose which will presently appear. If the first trunk is busy, relay 202, individual to said trunk, will be energized and a ground will be placed upon the terminal engaged by brush 117 and a circuit will be established througl'i the left-hand windings of relays 106 and 113 as previously described. When relay 106 energizes and locks up, the shunt around relay 107, through the back contact and outer lefthand armature of relay 106, will be opened and relay 107 will energize through its lefthand winding, brush 109, outer right-hand armature and normal contact of relay 108, back contact and left-hand armature of relay 101 to ground through the right-hand armature and alternate contact of relay 103. The energization of relay 107 causes the switch to take one step as previously described to engage the brushes thereof with the terminals individual to the second trunk leading to the attendants position. Should this trunk be busy the brushes of the switch will, nevertheless, come to rest upon the terminals of the trunk inasmuch as the lefthand winding of relay 107 is not now connected to brush 109. The calling subscriber will now receive a busy tone in the same manner as hereinbefore described and the switch will be restored to normal when the subscriber replaces his receiver upon the switchhook.

Assuming now that the first trunk is idle, the terminal engaged by brush 117 will be free from ground and relay 106 will therefore fail to energize, resulting in the deenergization of relay 113 and the extension of the calling subscribers line through the condensers 120 and 121 to the brushes 115 and 116, which are now in engagement with the terminals individual to the trunk. Ground is now extended, by the release of relay 113, from the front contact and outer left-hand armature of relay 103 through the normal contact of relay 104, back contact and outer left-hand armature of relay 113, brush 117 and the terminal engaged thereby, normal contacts of the holding key 204, lamp 205 and the normal contacts of the listening key 200 to grounded battery. The lamp 205 lights in this circuit and indicates to the attendant that a call is awaiting attention on this trunk. The attendant then operates the listening key 200 thereby extinguishing the'lamp 205 and establishing a holding circuit forslow to release relay 202. A circuit is now established for relay 101 extending from grounded battery through the right-hand winding of said relay, back contact and inner left-hand armature of relay 113, brush 118, and the terminal engaged thereby, and the contacts and armature of relay 202 to grounded battery. Relay 101 energizes to shunt the condensers 120 and 121 so that the calling line is supplied with talking current from the coil 203. The extension of the calling subscribers line through to the trunk establishes a circuit through the windings of coil 203 and the winding of the supervisory relay 201 which thereupon energizes-to establish an obvious circuit for slow to release relay 202. The energization of relay 101 also causes the release of relays 100 and 103 and closes a circuit traceable from grounded battery through the right-hand winding of relay 104, front contact and left hand armature of relay 101', and the inner armature and alternate contact of relay 103 to ground. This circuit is established before relay 103 can release its armatures after the deenergization of relay 100 and relay 104 will immediately lock up in a circuit extending through its inner right-hand armature and alternate contact, the back contact and outer left-hand armature of relay 113, brush 117 and the terminal engaged thereby and the left-hand contact and armature of relay 202 to ground. After the attendant at substation C has operated listening key 200, conversation may proceed with the calling subscriber through'the' non-inductive winding 206 of the supervisory relay 201. Should the attendant desire to hold the trunk after the calling party hangs up his receiver she may do so by operating the holding key 204 which will close an obvious circuit to maintain relay 202 energized. The release of the trunk is under the control of the calling party through supervisory relay 201 jointly with the attendant and is accomplished by the restoration of the keys 200 and 204 which results in the deenergization of relay 202 and the consequent removal of ground from the terminals engaged by brushes 117 and 118. The removal of ground from the latter brush releases relay 101 and when ground is taken from brush 117, the locking circuit of relay 104 is opened and this relay then deenergizes. The contact segment engaged by brush 119 is now grounded from the normal contact of relay 103 through the back contact and middle right-hand armature of relay 104 with the result that the switch is restored to normal in the same manner as previously described.

Calls to manual central ofiicc.

A subscriber within the private branch exchange may also secure direct connections to the central office by the transmission of two series of impulses, the first of which contains nine impulses and the second, ten. In response to the first series of im 3ulses, the brush 109 of the switch is engage with terminal 123 and in response to the second series the brushes ofthe switch are passed over the terminals individual to the attendants trunks and the second group of subscribers lines. The last impulse of the second series engages the brushes with the terminals individual to the first trunk leading to the central office. In the present instance, provision is made for three trunks leading to the central oifice and the terminals of all the trunks associated with brush 109, except the last one in the group, are connected to the left-hand Winding of relay 107. The terminals of all the trunks engaged by the brush 118 are permanently grounded so that immediately upon the seizure of an idle trunk and the deenergization of relay 113, relay 101 will operate to produce the same result as previously described.

It will now be assumed that all of the trunks extending from the private branch exchange terminate in a manual central oliice D. Should the first trunk engaged by the brushes of the switch individual to the calling line be busy, the terminal engaged by brush 117 will be grounded and relay 106 will operate, as before, to open the shunt for relay 107, which thereupon operates through its left-hand winding, the terminal engaged by brush 109 to ground at the inner armature and alternate contact of relay 103. The energization of relay 107 will cause the switch to take another step to engagethe brushes thereof with the terminals individual to the second trunk. In the event that this trunk is busy, the energization of relay 106 will again cause the operation of relay 107 in the circuit extending through brush 109 and the switch will he stepped to the terminals of the third trunk. Should this trunk be busy, relay 106 will again be operated, but, inasmuch as the lefthand winding of relay 107 is not connected to the ter minal of the third trunk engaged by brush 109, the switch. will fail to operate. A busy tone will, however, be'applied to the calling subscribers line in the same manner as formerly described, and the switch will be restored to normal upon the replacing of the receiver upon the switchhook at the calling substation.

Assuming now thatthe second trunk leadj ing to the central oflice'D is idle, relay 106 will not operate when its terminals are seized and relay 113 will then release to extend the calling subscribers line through the lefthand armatures of relay 300 to the windings of line relay 301. This latter relay then energizes to establish an obvious energizing circuit for slow to release relay 302 which, in closing its right-hand armature and front contact extends busy ground from the nor mal contact and left-hand armature of slow to release relay 303 to the terminal engaged by brush 117 to cause the multiple contact terminals of the trunk to test busy to all other individual switches. The energization of relay 302'also establishes an obvious circuit for the busy lamp 304 to indicate to the attendant that the particular trunk has been taken for use. The energization of relay 301 grounds the tip side of the trunk extending to central office through the right hand armature and front contact of relay 301 and the outer left-hand armature and back contact of relay 305. This I ground, in the present instance, is shown as extending from the back contact and inner armature of slow to release relay 500 but, inasmuch as the apparatus including the code switch shown in Fig. 5'is not employed in the case where the trunks all extend to a manual central oflice, it will be understood that this ground may be directly connected to the front contact and right-hand armature of relay 301. The operation of relay 301 also establishes a circuit for relay 306 extendin from grounded battery through the winc ing of this relay, the right-hand normalcontacts of release key 307, the normal contact of dialing key 308, the alternate contact of relay 306 and the front contact and left-hand armature of relay 301 to ground. Relay 306 energizes and locks in a circuit through its alternate contact and outer left- .hand armature to ground at the left-hand armature and front contact ofrelay 302.

The grounding of the tip side of the trunk by the operation of the relay 301 causes the energization of line relay 319 atthe central office D, whereupon the line lamp at said office individual to the trunk is lighted. The Operator then answeres the call by inserting a plug into the jack of the trunk in the usual manner. This operation closes a circuit extending from grounded battery in the cord circuit employed by the operator, through the middle normal contact of the flashing or disconnect key 309 which may be used for recalling the central oflice operator or giving a disconnect signal, the inner right-hand armature and back contact of relay 310, the windings of line relay 311,

the upper normal contact of key 312 and the left-hand normal contact of key 309 to ground in the operators cord circuit. The energization of relay 311 establishes an obvious circuit forthe slou to release relay 303, which, in attracting its left-hand armature, disconnects busy ground from the front contact and right-hand armature of relay 302 and extends it directly through the alternate contact of relay 303 to the brush 117 and to the lamp 304.

Relays 303 and 306 now being energized, a circuit is established for relay 300 extending from grounded battery through the winding of said relay, the lower normal contact of key 312, conductors 313 and 314- which are strapped together when the trunks lead to a manual ofl ice, front contact and inner left-hand armature of relay 306 and the right-hand alternate contact of relay 303 to ground. Relay 300 energizes to extend the calling line over the trunk to the central oflice, whereupon communication over the trunk may proceed. The energization of re lay 300 opens the circuit for relay 301 which then releases, but relay 302 is maintained energized from the front contact and righthand armature of relay 300. Upon the energization of relay 300, the trunk supervisory relay 315 is energized to establish an obvious circuit for relay 310. The energization of the latter relay opens the encrgizing circuit for line relay 311 which then releases and relay 310 also bridges the noninductive shunt 316 around the active winding of the supervisory relay 315.

At the termination of the conversation, the restoration of the receiver upon its switchhook at the calling substation releases the supervisory relay 315 which, in turn, causes the deenergization of relay 310. Relay 311 is then energized over its previously described circuit, thus preventing the release of relay 303. As a winding of relay 311 is of a high resistance, the supervisory relay at the central ofiice is released thus giving the operator the disconnect signal in the usual manner. When the operator removes the plug from the jack, relay 311 releases and causes, in turn, the release of relays 303, 300, 302, 306 and the extinguishment of busy lamp 304. The trunk circuit is now restored to normal and the removal of ground from brush 117 causes the release of the individual switch in the same manner as previously described. Should the op erator at the central ofiice disconnect before the calling subscriber replaces his receiver upon the switchhook, relays 315 and 310 will release, but line relay 311 will fail to operate. This permits of the release of relays 303 and 300. Upon the restoration of the latter relay, relay 301 will again energize to prevent the release of relays 302 and 306 and to again connect ground to the tip side of the trunk leading to central office where upon the line lamp thereat will again light.

The attendant may call the manual office D by operating the listening key 317 which extends ground from the right-hand normal contact and armature of relay 303, to the tip side of the trunk, with the result that line relay 319 at the central oflice will operate to light the line lamp. The closure of the outer right-hand contact of key 317 extends ground therefrom through the'righthand normal. contact of key 309, and from thence in parallel through the back contact and right-hand armature of relay 327 and the windng of relay 305 to light the guard lamp 320 and energize the latter relay. The euergization of relay 305 extends ground from the outer right-hand contact of key 317 through the front contact and inner lefthand armature of relay 305, and the normal contact of relay 31.8 to the multiple test terminals of the trunk to provide a busy test therefor. This ground is also extended throughthe lamp 304 to grounded battery to light said lamp to indicate the busy con- .dition of the trunk. The central office operator, observing the lighted condition of the line lamp individual to the trunk, answers the call by inserting a plug into the jack of said trunk, whereupon supervisory relay 315 is included in series with the line and thereby energized. The operation of this relay causes the energization of relay 310 which, in. closing its inner right-hand armature and front contact includes the non-inductive winding 316 of the supervisory relay in the circuit for talking purposes. The energization of relay 315 also closes an obvious circuit for relay 3.03 which, in energizing, removes ground, extending from the normal contact thereof, from the tip side of the trunk.

The attendant may release the trunk by operating the disconnect key 309 and by restoring key 317 which removes ground from the multiple test terminals and causes the deenergization of relay 305 and the extinguishmentof. lamps 304 and 320. The re placing of the receiver upon itsswitch hook at the attendants substation C opens a circuit of the supervisory relay 315 which thereupon releases to cause the deenergization of relay 310 and relay 303. The central ofiice operator, upon receiving the disconnect signal in the usual manner, removes the plug from the jack.

Calls from manual central 077500.

On an incoming call from the manual central oflice D to the attendant at substation C, the operator at central office inserts the cuit, the ring side of the trunk, the middle normal contacts of key 309, the inner righthand armature and back contact of relay 310, the high and low resistance windings of relay 311, the middle normal contacts of key 312, the tip side of the trunk and lefthand normal contacts of key 309 to ground in the operators cord circuit. Relay 311 energizes and through its armature and contact closes an obvious circuit for relay 303 which, in energizing, lights the busy lamp 304 and extends a busy groundto the multiple terminals of the trunk. When the central oflice operator applies ringing current to the line, the same extends through the righthand winding of relay 322 and the outer right-hand armature and back contact of relay 306 to energize relay 322,which thereupon locks up in a circuit extending from grounded battery, through the lefthand winding and contacts of relay 322, back contact and inner left-hand armature of relay 305, the normal contact of relay 313 and the left-hand alternate contacts of relay 303 to ground. A circuit is also established to light the line lamp 323 extending from grounded battery, through said lamp, the armature and left-hand contact of relay 322, and from thence over the locking circuit of said relay. The attendant at substation C, observing that a call is awaiting attention, first operates listening key 317 which energizes relay 305 and lights the guard lamp 320 as previously described. The energization of relay 305 opens the locking circuit for relay 322, whereupon said relay releases and lamp 323 is extinguished. The energization of relay 305 also bridges the left and right-hand windings of retardation coil 324 across the trunk through the low resistance winding of the line relay 311 in parallel with the high resistance winding to hold the trunk, the middle winding of said coil 324 being normally shunted through the lefthand armature and contact of relay 310. The attendant now removes the receiver from its switchhook at her substation, where upon supervisory relay 315 will operate in series with the battery in the cord circuit. The operation of relay 315 again operates relay 310 to close the talking circuit and open the shunt around the middle winding of retardation coil 324. Relay 311 releases to open the original energizing circuit for relay 303 but this relay is maintained energized by the ground at the armature and contact of relay 315. The attendant may converse with the central otlice operator and if the call is to be extended to a subscriber within the private branch exchange, the attendant leaves the listening key 317 operated and actuates dialingkey 308. For a purpose which willpresently appear, it is to be noted that the lower contacts of the key 303 are adjusted to open before the other ones close. The closure ofthe upper contacts of said dialing key .establishes an obvious circuit for relay 321 to extend the attendants telephone set through the lower armatures and alternate contacts of said relay. A circuit is then established through the windings of line relay301 and lefthand armatures and normal contacts of relay 300, and relay 301 energizing in this circuit, establishes an obvious circuit for relay 302.

hen relay 321 operates, relay 315 and 310 release. This causes the operation of relay 311 and the inclusion of the left and righthand windings of the retardation coil 324 in the trunk since relay 305 is operated and the central office supervisory relay therefore remains energized. The release of relay 310 again. shunts the middle winding of the coil 324 and the energization of line relay 311 prevents the release of relay 303. Inasmuch as the lower contacts of key 308 are opened before the upper ones are closed, relay 306 will not operate upon the energization of the line relay 301. The operation of relays 302 and 321 closes the circuitfor the stepping relay 400 extending from grounded battery through resistance 401, the left-hand winding of relay 400, brush 402 in its normal position, the right-hand armature and alternate contact of relay 404, the back cont-act and outer left-hand armature or relay 405, contact and upper armature of relay 321 and the left-hand armature and front contact of relay 302 to ground. The left-hand winding of relay 400, is, however, normally short circuited by ground extending through the front contact and right-hand armature of relay 301 and'the outer left-hand armature and front contact of relay 305 so that relay 400 will not operate.

The attendant now actuates her impulse sending device to transmit the required number of impulsesto connect the switch shown in Fig. 4 to the terminals individual to the called line and at each interruption of the circuit for relay 301 the short circuit .is re moved from. the left-hand winding of relay 400 and this relay thereupon operates. In so doing, circuits are established through the left-hand armature and contacts of this relay for motor magnet 403 and slow to release relay 404. The energization of relay 400 also establishes a locking circuit for itself through its right-hand winding, front contact and right-hand armatureand the armature and contact of' motor magnet 403 and this locking circuit is maintained until the motor magnet completes its stroke, at which time its contact is opened. This permits the stepping relay 400 to remain operated should the short circuit for its left-hand winding be closed before the switch has completed its stepping. The operation of relay 404 prepares, through its outer alternate contacts, a circuit for the left-hand winding of the stepping relay so that after the brushes of the switch have been stepped from their normal position, the stepping relay will operate in response to further impulses. The energization of relay 404 also establishes a circuit extending from grounded battery through resistance 407, the left-hand winding of relay 406, the inner alternate contact and inner armature of re lay 404 and the left-hand alternate contact of lay 303 to ground. Relay 406 energizes in this circuit and disconnects the brushes 408, 409, 410 and 411 from their associated circuits to prevent the switch from disturbing the lines over which it passes. At the termination of the impulses, relay 301 remains operated and thereby releases relay 400, which, in turn, deenergizes relay 404 and the switch then comes to rest upon the terminals of the called line.

It will be obvious from the foregoing description that the switch shown in Fig. 4 operates in substantially the same manner as the subscribers individual switch and that therefore the transmission of one or two series of impulses by the attendant will engage the brushes of the switch with the terminals of the called line.

If the called line is idle when the attendant calls, no ground will be found upon the terminal engaged by test brush 410 and upon the release of relay 404, relay 406 will be deenergized to extend the talking circuit of the trunk to the called line. The release of relay 406 also extends the ground from relay 303 through the back contacts and left-hand armatures of relay 406 to brushes 410 and 411. The ground on brush 410, which is now in engagement with terminal 1055, assuming that substation A is called, is extended through the innermost normal contacts of relay 106 the alternate contacts of relay 104, the left-hand armature and back contact of relay 103 and the'winding of cutoff relay 102 to grounded battery. Relay 102 energize-s and, in the same manner as described in connection. with a call to substation B, ringing current is applied through the left-hand winding of relay 104 to the ringing apparatus at substation A. The current passing through the left-hand winding of relay 104 at this time is not sufficient to cause the energization of this relay but, upon the removal of the receiver at the called substation, the flow of current through said left-hand winding is suflicient to cause the relay to attract its armatures, whereupon the same locks up through its right-hand winding, inner right-hand armature and alternate contact and from thence over the energizing circuit for relay 102.

The response of the called subscriber extends the line through brushes 408 and 409 to the relay 301 so that this relay remains energized together with relay 302 when the attendant restores the keys 308 and 317 to open the original energizing circuit of relay 301. The restoration of key 308 causes the release of relay 321 and closes previously described circuit for relay 306 which extends to ground at the front contact and left-hand armature of relay 301. Relay 306 locks up through its alternate contact and outer left-hand armature to ground at the left-hand armature and front contact of relay 302. Relay 303 already being energized, upon the energization of relay 306 a circuit is established for relay 300, extending from grounded battery through the winding of relay 300, the lower normal contacts of key 312, conductors 313 and 314, which are con nected when the private branch exchange has access to a manual ofiice, front contact and inner left-hand armature of relay 306 and the alternate contacts of relay .303 to ground. Relay 300 energizes to extend the line through to the calling trunk and in so doing opens the energizing circuit for relay 301. Relay 302, however, remains operated owing to the ground at the front contact and right-hand armature of relay 300. The

supervisory relay 315 is now in series with the called line and operates to energize relay 310 which then extends thecalled line to the central office and bridges the non-inductive Winding 316 across the supervisory relay 315. Since relays 305 and 306 are now energized, relay 318 is operated over a circuit extending from grounded battery, through the left-hand winding of said re lay, the middle left-hand armatureand front contact of relay 305, the front contact and inner right-hand armature of relay 306 and the front contact andouter right-bane armature of relay 310 to ground; Relay 313 locks up through its right-hand winding, armature and front contact, the lefthand normal contact of release key 307 and the left-hand alternate contacts of relay 303 to ground, whereupon the control of the locking circuit for relay 305, extending through the front contact and inner left-hand armature of said relay, is transferred from relay 303 to relay 310. The energization of relay 318 establishes an energizing circuit for slow to release relay 327 extending from grounded battery, through the winding of said relay, the front contact and inner left hand armature of relay 318 and from thence to ground over the previously described energizing circuit for the latter relay. The energizkation of relay 327 extinguishe s the guard lamp .320. I H

The attendant may cut or the called substation and talk to the central office operator by operating the keys 317 and 312, the latter key causing the release of relay 3 00 and thereby disconnectin the called substation from the central office. The release o f re- 1551' 300 will again cause the energization of relay 301 and hence relay 302 will remain operated. The restoration of key 312 again operates relay 300 to extend the line through to the central ofiice. c

To release the trunk in the event that the attendant has not secured the connection to the called line, key 317 is restored and re lease key 307 operated. The operation of the latter key extends ground from the lefthand alternate contacts of relay 303, through the alternate contact of key 307, brush 412, the continuous off normal segment associated therewitlrand the righthand windings of relays 405 and 406, in parallel to grounded battery. The energization of relay 405 extends ground from relay 303 through the outer right-hand armature. and front contact of relay 405 to the back contact and right-hand armature of relay 400 and from thence through the armature, contact and winding of motor magnet 403 to establish a self-interrupting circuit for the motor magnet whereby the brushes of the switch will be stepped to normal, at which time the energizing circuit for relays 405 and 406 will be opened and the switch will be in its normal condition. The operation of the release key 307 also releases relays 306, 318 and 327 and the release of the relay 306 results in the deenergiz ation of relay 300, whereupon the line extending between the called substation and 'central office is opened. Relay 300, in releasing, causes the deenergization of relay 302. The restoration of key 317, which con nected. the attendants substation to the cen tral office causes the release of relays 315 and 310. hen relays 306 and 318 release, the locking circuit for relay 305 is opened and this relay releases as soon as relay 303 restores, which occurs upon the release of relay 315. The deenergization of relay 305 removes the holding bridge through the retardation coil 324. The disconnection at the central office is made in the usual well known manner.

If the line called is busy, the ground on the test terminal will cause the energization of relay 405, upon the release of relay 404, over a circuit extending through brush 410, the outer left-hand armature and front contact of relay 406 which is energized at this time, the inner left-hand armature, the alternate contact and left-hand winding of relay 405, the inner contacts of relay 404, the left-hand winding of relay 406 and the resistance 407 to grounded battery. Relay 405 energizes and locks up over its lefthand winding and alternate contact, through. the left-handnorrnal contact of key 3.07 and the left-hand alternate contacts of relay 303 to ground. Relays 405 and 406 are held energized and the energization of the former, relay connects busy tone apparatus to the attendants tel- '1 ice phone, whereupon she may restore the apparatus to normal in the same manner as above described.

In case the subscriber wishes to recall the private branch exchange attendant after his line has been connected to and the attendant is attending to other calls, he depresses his switchhook momentarily or may operate his calling dial. This releases relay 310 momentarily, unlocking and releasing relay 305. Relay 327, being slow to release, remains operated on the momentary release of relay 310, and the bridge through coil 324 is not opened to cause the operation of the disconnect signal at the central oflice. The release of relay 305 with relay 318 operated connects lamp 323 with the contact of relay 310 so that this lamp remains lighted as a recall signal when the line circuit remains closed. The circuit for lamp 323 is as follows: battery, lamp 323, outermost 318, innermost left armature and normal contact of relay 305, middle left armature and alternate contact of relay 318, inner right armature and alternate contact of relay 306, outer right armature and alternate contact of relay 310 to ground.

The attendant now operates the listening key which operates relay 305 to extinguish the lamp 323. The attendant may transfer the call to another station by operating the release key 307. This releases the operated relays and another line may be selected in exactly the same manner as described in connection with Fig. l.

The attendant at substation C may call any subscriber within the private branch exchange independent of any one of the central ollice trunks by first opera-ting key 207 which connects the substation to line relay 208 which thereupon. energizes to cause the operation of slow to release relay 209. A circuit is then established extending from grounded battery through :the left-hand winding or stepping relay 210, brush 212, the right-h and armature and normal contact of .slo w to release relay 211 and the righthanl armature and alternate contact of re- 7 lay 209 to ground. With relay 208 energized, relax 210 will not operate in the cir cuit just described for the reason that the left-hand winding thereof is short circui-ted pulse sending device to transmit the required number of impulses for establishing 'a connection to the wanted line, relay 208 responds to each interruption of the line circuit and thus removes the short-circuit from the left-hand winding of relay 210 which thereupon operates. The closure of the contacts and the left-hand armature of the latter relay establishes circuits for motor magnet 213 and slow to release relay 211., which latter relay remain-s energized during the transmission of impulses. Relay 210 locks through its right-hand winding, front contact and right-hand armature, the armature and contact of motor magnet 213 and the contact and left-hand armature of relay 210 to ground. This locking circuit is maintained until the motor magnet has completed its stroke. At the termination of the impulse, relay 208 again energizes to short circuit the left-hand winding of relay 210 and this operation continues until the brushes of the switch are engaged with the terminals individual to the called line. Upon the energization of relay 211, when the impulses are first transmitted, a circuit is established for relay 214 extending from ground through the alternate contact and left-hand armature of relay 209, the inner armature and alternate contact of relay 211 left armature and alternate contact of relay and the left-hand winding of relay 214 to grounded battery. Relay 214 energizes and disconnects brushes 218, 219, 220 and 221 from their associated circuits. The energization of relay 211 also connect-s ground from the alternate contact and right-hand armature of relay 209, through the righthand alternate contacts of relay 211 to the left-hand winding of relay 210 so that this relay will continue to operate after brush 212 has moved from, its normal position. If two series of impulses are transmitted. the first series will engage brush 212 with the fifth terminal shown in the bank of the switch. and upon the first impulse of the second series being transmitted, relay 210 will be again operated through brush 212 in the same manner as described in connection with the operation of the switch individual to the subscriber shown in Fig. 1. At the termination of the impulses rolay 208 remains operated thereby releasin relay 210 which, in turn, causes the dccucr gization of relay 211.

If the called line is idle, relay 214 roleases upon the deenergization of relay 211 since no ground will be found upon the terminal engaged by brush 220. Ringing current will then be applied to the called line in the same manner as previously described and conversation may now proceed between the attendant and the subscriber.

If the called line is busy, ground potential on brush 220 will be extended through the outer left-hand armature and front contact of relay 214, the left-hand armature, normal contact and left-hand winding of relay 215, the inner right-hand normal contacts of relay 211 and the left-hand winding of re- 214 to grounded battery. Relay 214 will thus remain energized and relay 215 will operate and look through its left-hand winding and alternate contacts, the left-hand normal contacts of key 216 and the righthand armature and alternate contact of rejlay 209 to ground. The operation of relay 215 "connects busy itone apparatus 217 to the attendants telephone set, whereupon she may replace her receiver upon its switchhook to accomplish the release of the switch in the same manner as set forth in connection with the operation of the switch shown in Fig. 1. The attendant may, if the line is busy, connect her set to the line by operating key 216 which disconnects the busy tone from substation C- and connects the attendants line to brushes 218 and 219. The operation of key 216 opens the original locking circuit for relays 21 i and 215 and transfers this locking circuit from relay 209 to brush 220 from which ground extends through the outer left-hand armature and front contact of relay 214E, left-hand altera ears contact of key 216, alternate contacts and left h an'd. winding of relay 215, and from thence over the previously described locking circuit. If ground is removed from brush 220 under this condition, relays 21 i and 215 release and thereby extend the talking conductors in the regular manner and again ground brushes 220 and 221 whereupon ringing current will be applied to the called line as formerly set forth.

Calls to automatic central ofi'ice.

The extension of a calling subscribers line to a central ofiice trunk when said trunks terminate in a machine switching office will now be described. Under this condition, the attendant at the private branch exchange has supervision over certain calls by the subscribers which are extended to the machine switching central o'tlice. For this purpose, there is provided a code circuit including a switch, shown in Fig. 5, which is responsive to impulses transmitted from the calling subscribers substation to said oflicje to cause a signal to be operated before'the attendant to notify her that a call on one of the central oflice trunks is awaiting supervision. If the call is one that does not require the attendants supervision, other conditions take place in the code circuit which prevents the signal be ing operated before the attendant. In this instance, the impulse are simply repeated to the central oiiice to operate the switches thereat whereby the call is extended to the desired station, Inasmuch as the switches at the central otfice form. no part of the present invention, and asthey may be of any desired construction well known in the art, 'no attempt has been made to illustrate the same. v

When a subscriber within the private branch exchange operates his individual switch E'shbw n in Fig. 1 to select a trunk leading'to the central office, relays e01, 302 and h si -crate -as pen-easy described. The

operation of relay 301 extends ground at the back Contact and inner armature of relay 500 to the tip side of the trunk leading to the central oflice, whereupon a selector switch will operate to engage the terminals of the selected trunk. A circuit is then established which extends through the windings of the line relay 311 in the trunk circuit, which relay, in energizing, operates relay 303. Upon the closure of the right-hand alternate contacts of the latter relay, conductor 31 i is grounded through the inner left-hand armature and front contact of relay 306. At the same time ground at the right-hand alternate contact of relay 308 is extended to conductor 329. The grounding of conductor 314i establishes an energizing circuit for slow-to-release relay 500 extending through the back contact and left-hand armature of relay 514C. Relay 500 in closing its inner armature and front contact bridges the conductors 325 and 326 across the trunk through the right-hand armature and contact of line relay 301 so that when this relay vibrates its armatures in response to the transmission of impulses from the calling substation, the impulses will be repeated through this bridge to the central oflice to operate the switches thcreat. The energization of relay 500 also establishes a circuit for the stepping relay 502 extending from grounded battery through resistance 501, the left-hand arniiature and front contact of relay 500 and the left-hand winding of relay 502 to ground. This winding of relay 502 is short circuited by ground extending from the left-hand armature and contact of relay 301 over conductor 328 so that relay 502 will not operate upon the energization of relay 500. V

hen the calling subscriber transmits the first series of impulses corresponding to the first digit of the called number, the circuit of relay 301 is interrupted so that impulses will be repeated to the central oliice and the short circuit remfoved from the left-hand winding of relay 502. This latter relay, therefore, responds to each removal of the short circuit by attracting its armatures. The closure of the left-hand armature and contacts of relay 502 establishes circuits for slow-to-release relay 503 and motor magnet 1-, the circuit for the latter being through the resistance 505. In energizing, relay 502 looks up through the armature and con tact of relay 50 and remains in this condition until'the contact and armature of motor magnet SO L-is opened which occurs at the end of the stroke. Normally, the ground extending from the right-hand alternate contact of relay 803 over the conductor 329 is applied to brush 507 of the code switch. hr'ough the normal contact of relay 503 and the outer righthand armature and back Contact at relay 51 2, and brush 5'06 all run

grounded from the contact and the righthand armature of relay 503. WVhen the latter relay energizes, ground on conductor 329 is extended through the left-hand armature and alternate contact of said relay through conductor 517, branches to which are associated with the relays of contacts over which brushes 508 and 509 pass.

When employing the code circuit and it is desired that the attendant have supervision over certain calls the contacts of the code switch bank over which brushes 508 and 509 pass and which correspond to certain digits of such calls are connected to the conductor 517, otherwise these contacts are not so connected. The contacts or terminals associated with each of the brushes 508 to 511, inclusive, are divided into two groups separated by a vertical intermediate row of contacts including contacts 520. As shown in Fig. 5 it will thus be seen that each of the groups contain three contacts or terminals, the remaining terminals of the groups being omitted for simplicity and economy of space.

In the operation of the code switch, through connections between conductors 517 and 519 to the terminals of the switch traversed by brushes 508, 509 and 511 such switch is caused to continue its operation until the complete code has been transmitted after which circuits are closed to light the line lamp associated with the trunk employed thus calling in the operator. The connection through the central office is not disturbed except at the instance of the operator. In case a code is transmitted which does not require the operator to be brought in, as when the brushes of the code switch encounter terminals to which no connection t conductor 517 or 519 is made then the code switch ceases its operation and a connection between the calling subscribers line and the central office trunk is established so that the impulses are not then repeated by relay 301 but are transmitted directly. As an example of the operation of the code switch, a four-digit code connection will now be described.

In response to the series of impulses corresponding to the first digit dialled the code switch is stepped to engage the brush 508 with a terminal in the first group of contacts associated therewith. If the contact then engaged by said switch is connect ed to conductor 517, relay 512 will be energized over a circuit extending from grounded battery through the winding of said relay, the outer right hand armature and back contact of relay 515, brush 508 and the contact engaged thereby, conductor 517, and from thence to ground on conductor 329 through the left hand armature and alternate contact of relay 503, this circuit being established before relay 503 releases at the termination of the series of impulses. hen relay 503 releases a locking circuit for relay 512 is established from grounded battery through the winding, frontcontact ancl outer right hand armature of said relay and the normal contact of relay 503 to ground on conductor 329. lirush 506 is now engaged with segment 521 and when relay 503 releases ground is extended through its right hand armature, brush 500, segment 521, winding of relay 513 to grounded battery, this relay being adjusted for both slow operation and release. The closure of the front contact of relay 513 tablishes a self-interrupting circuit for metor magnet 50% extending from grounded battery through the resistance 505, winding. contact and armature of magnet 504:, right hand armature and back contact of relay 502, front contact and armature of relay 513, segment 521, brush 506, armature and back cont-act of relay 503 to ground. The motor magnet then operates to step the switch until the brush 506 engages contact 520 whereupon the operating circuit for aid motor magnet will be opened and the switch will come to rest. The second series of impulses is now transmitted and relay 503 again operates in response to the first energization of relay 502 to open the locking circuit for relay 512 which then releases. Motor magnet 50 i is operated in response to the energization of stepping relay 502 and the brushes of the switch are then stepped to the contacts of the second group. Brush 506 is now in engagen'ient with seg ment and brush 503 with a contact in the second group associated therewith. If this latter contact is connected to the left hand armature and alternate contact of relay 503 through conductor 517, relay 5'12 again operates and locks up in the same manner as previously described and relay 513 again operates to close the previously mentioned self-interrupting circuit for inotor magnet 504 whereupon the switch is stepped to its normal position. Upon reaching this position the right hand armature of relay 503 is connected through the brush 506 and its normal contact, the inne left hand armature and front contact of relay 512, the back contact and outermost right hand armature of relay 514, the winding of relay 515 to grounded batteryv T he latter relay energizes in this circuit and locks up through its front contact and left hand armature and the normal contact of relay 514E to grounded conductor 329. The energization of relay 515 transfers the operating circuit for relay 512 from brush 508 to brush 509 through the outer right hand armature and front contact of relay 515.

The series of impulses corresponding to the third digit of the called number is now transmitted and the code switch again opcrates to engage its brushes with the associated contacts of the first-group. With relay 515 energized and locked up, should brush 509 engage a contact in the first group connected to conductor 517, relay 512 will then energize through the outer right hand armature and front contact of relay 515 and will lock up when relay 503 releases at the termination of the series of impulses. With brush 503 in engagement with segment 521, relay 513 operates as before to cause motor magnet'504 to step the brushes of the switch to the intermediate row of contacts including contact 520.

The fourth digit of the desired number is now dialled to again step the brushes of the code switch over the second group of the associated contacts. The contacts of the second group over which brush 509 passes and which correspond to certain ligits of numbers requiring supervision are connected to the conductor 517. Such contacts as just mentioned in the second group associated with brush 511 are connected to coi'iductor 519 which extends to the right hand wind ing of relay 514. Therefore, should brushes 509 and 511 engage such'contacts as men tioned above when the switch is brought to rest at the termination of the fourth set of impulses, relay 512 again energizes and locks up and upon the release of relay 503,

relay 513 again energizes. This relay being slow to operate, a circuit is closed before said relay can open its back contact, which circuit extends from ground through theright hand armature and contact of relay 503, brush 506, segment 522, the armature and back contact of relay 513-, the inner right hand armature and front contacts of relays 512 and 515, brush 511 and the contact engaged thereby, conductor 519, and the right hand winding of relay 514 to grounded battery. Relay 514 energizes in this circuit and locks up through the right hand'winding, innermost right hand armature and alternate contact to ground on the conductor 329. The energization of 'relay 514 opens the energizing circuit for relay 500 and the locking circuit for relay 515 and these relays thereupon release. Relay 512 being still energized and locked up, ground on conductor 329 is xtended through the normal contact of relay 503 which releases at the tern'iination of the series of impulses through the outer right hand armature and front contact of relay 512, front contact and middle right hand armature of relay 514, con-- ductor 330, back contact and outermost left hand armature of relay 318 and the line lamp 323 to grounded battery. The line lamp is lighted in this circuit to inform the attendantthat the call requires supervision.

l ihen relay 513 energizes upon the release of relay 503, motor magnet 504 is again operated to return the switch to its normal position. The energization of relay 514 connectsconducto-rs 313 and 314 through the left hand armature and front contact of said relay and a circuit is thereby-established for relay 300 extending from grounded battery through the winding of said relay, the lower normal contact of key- 312, conductor 313, front contact and left hand armature of relay 514, conductor 314, front contact and inner left hand armature of relay 306 and the alternate contact of relay 303 to ground. The energization of relay 300 extends the calling line over the trunk to the central oiiice. The release of relay 500 upon the energiz ation of relay 514 opens the bridge through which the impulses were repeated to the central office and again grounds conductor 325, but the relay 500 being slow to release holds this bridge closed until the line is extended by the operation of relay 300. In this manner a connection which requires the supervision of the operator is established upon the operation of relay 300. The calling subscribers line is directly connected to the central office trunk so that further trains of impulses may be directly transmitted without being repeated at the right hand armature and contact of relay 301.

If at any stage in the selection of a called linethe code switch stops with its brushes 508 and 509 in engagement with contacts not connected to conductor 51 7, relay will not energize and the release of relay 503 at the termination of the series of hu pulses grounds the brush 507 through the outer right hand armature and back contact of relay 512 with the result that this ground is extended over conductor 519 to grounded battery through the right hand winding of relay-51:4. The latter relay energizes with the same result as previously described and prevents any further operation of the code switch. Under the circinnstances justreferred to if the contact not connected to conductor 517 is located in the first 'rou 3 the much as relay 512 is not operated relay 513 will remain energized through the back con tact *and outer left hand armature of relay 512, conductor 520, and the brush 506 to ground at the right hand armature of relay 503 and motor magnet 504 will therefore continue to step brushes of the switch to their normal positions.

lVhen relay 300 energizes to extend the calling line through to the central oflice the supervisory relay 315 is included in the line circuit and is energized to close the cues gizing circuit forrelay 310 which disconnects line relay 311 from the line circuit to cause the release thereof. is now held energized under the control of the Relay gization of relay 300 but relay 302 remains, energized under the control of relay 300.v

Thus, it will be seen that when a code is dialed which does not require the serviceof an operator the calling subscribers line is directly connected to the central oiiice trunk and the code switch is returned to normal. Returning now tothe previously described case where the attention of the operator was attracted by the lighting of the line lamp 323, the manner in which such operator supervises the connection will be described. 'Whencthe attendant operates listening key 317 in response to the lighting of the lamp 323, relay 305 energizes and causes the energization of relay 318 over a circuit'previously described therefor. Relay 318 locks up and closes the energizing circuit for relay 327 to open the energizing circuit of the guard lamp 320. The energization of relay 318 opens the energizing circuit for the line lamp323 which is then extinguished. The closure of the right hand contact of listening key 31'Zalso extends ground through the left hand winding of relay 51 1 over conductor 331 to provide an additional holding circuit for this relay. When the trunk is released at the end of the call restoration occurs'as before and the release of relay 303 opens the locking circuits for relays 512 and 51 1, the former relay having remained energized after the last series of impulses which were transmitted in extending the call. With the release of relays 512 and 514 the code circuit is then in its normal condition and ready to be operated upon the extension of another call to the central ofiice.

To arrange the circuit to respond to three instead of four digit numbers the necessary contacts in the first group associated with brush 511 are connected to conductor 519 so that relay 51 1 will operate through the front contacts and inner right hand armature of relays 515and 512 before relay 513 is dialed to open its back contact. This switch then stops with the brushes in engagement with the intermediate vertical row of contacts and remains in this position until the trunk is released and relay 503 deenergized whereupon the locking circuit for relay 512 will be opened and this relay released. Relay 513 is then operated through the back contact and outer left hand armature of relay 512 with the result that the switch is stepped to normal as before.

Vhen arranged to operate in conjunction with numbers containing both two and three digits, relay 516 is provided and is adapted to be connected through brush 510 to con tacts in the first group corresponding to the first digit of the two digit numbers to which the circuit is to respond. Therefore, upon the transmission f the impulses for the first digit, relay 512 operates through brush 508 and the contact engaged thereby which is connected to conductor 517. Relay 512 locks up as before and upon the release of relay 503 a circuit is momentarily closed before relay 513 can energize and open its back contact, said circuit extending from grounded battery through the winding of relay 516, brush 510, and the contact engaged thereby which corresponds to the contact from the first group associated with brush 508, conductor 513, back contact and armature of relay 513, segment 521, brush 5% and the right hand armature and contact of relay 503 to ground. Relay 510 energizes and locks up through its contact and righthand armature and the alternate contact of relay 51 1 to ground on conductor 329. Upon the energization of relay 513 the switch is stepped as before to engage the brush 500 with the terminal 520 and the ground on said brush from relay 503 is then extended through the outer left hand armature and front contact of relay 512, left hand armature and contact of relay 516, back contact and outermost right hand armature of relay 51 1, winding of relay 515 to grounded battery. Relay 515 energizes and locks up through its front contact and left hand armature to ground on conductor 329. The second digit of the two digit number is then dialed and brush 511 is stepped to the proper contact for the second digit located in the second group and connected to conductor 519. The circuit then functions in the same manner as described in connection with the fourth digitof a four digit number.

Should a three digit number be dialed no contact in the second group associated with brush 511 is connected with conductor 519 when the second series of impulses is sent. Relay 514 will therefore not energize the end of the second series of impulses and the switch will be stepped to normal. The proper contact in the first group associated with brush 511 .is connected to conductor 519 and the switch then operates as previously described in connection with the three digit numbers.

The code switch may be made to operate to light the line lamp 323 by the transmission of a singie series of impulses. in this case the proper contact in the lirst group associated with. brush 508 is connected to conductor 51'? and the corresponding con tact in the first group associated with brush 510 is connected to the right hand winding of relay instead of to relay 516 through conductor 518. When relay 512 operates and locks up as before ground is momentarily extended until relay 513 operates upon the release of relay 103 from the right hand armature of this relay through the brush 506 segment 5" armature and back con tact of relay 513, conductor 518, contact enlllh lll)

protest gaged by brush 510 and from thence through the left hand winding of relay 514 to grounded battery. Relay 514 then operates as before to light the line lamp 323. The

switch is then s te oped to connect the brushes thereof with the intermediate vertical row oi contacts where the same stops unt1l the trunk is released and relay 508 deenergized.

described.

Call; from automatic central 077206. On; an incoming call from the central oiiice, the attendant is signaled in the same manner as previously described and upon 'the operation of relay 308 in the trunk circuit, conductor 329 is grounded but conductor 314iis not grounded since relay 306 does not operate on the incoming call. When the attendantanswers the call by operating listening key 317, ground, from the inner right-hand contact of said key is extended over conductor 331 and through the left-hand winding of relay 514 to grounded battery to energize this relay, whereupon the same loclrs up to ground on the conductor 329. The operation or" relay 514- prevents the code, circuit from operating as relay 500 cannot now he energized.

l Vhat is claimed is:

l. in a telephone system, a calling line, a switch for extending said line having directive and automatic movements, a crush for said switch having a normal position, a stepping circuit for said switch controlled through said brush when the same is in its normal position, a relay through contacts of which said stepping circuit is also controlled, means responsive to impulses for rendering said stepping circuit effective to step the switch. in a directive movement,

means whereby said stepping circuit is con-' trolled through contacts of said relay independently of said brush after the latter is stepped from normal and during the dircctive movement of said switch, and means for returning said stepping circuit to the joint control of said brush and relay dur-' ing an automatic: movement of said switch.

2. In a telephone system, a calling line, switch for extending said line having directive and automatic movements, a brush for said switch having a normal position, groups of interspersed lines and trunks having terminals over which said brush passes, a stepping circuit for said switch controlled through said brush when the same is in its normal position, a relay through contacts ot'wl'ii'ch said stepping circuit is also controlled, means responsive to impulses for rendering said stepping circuit effective to step the switch in a directive movement to select a line or trunk, means whereby said stepping circuit is controlled through contacts of said relay independently of said brush after the latter is moved from normal and during the directive movement of said switch, and means for returning said stepping circuit to the joint control of said brush and relay during an automatic movement of said switch.

3. In a telephone system, a calling line, a switch for extending said line having directive and automatic movements, a brush for said switch having a normal position, a stepping circuit for said switch controlled through said brush when the same is in its normal position, a relay through contacts of which said-stepping circuit is also con trolled, means responsive to impulses for rendering said stepping circuit effective to step the switch in a directive movement, means whereby said stepping circuit is con trolled through. contacts of said relay in dependently of said brush alter the latter is stopped from normal and during the di rective movement of said switch, a testing relay for saidswitch, and means for returning said stepping circuitto the joint control of the first named relay, said brush and the last named relay during an automatic movement of said switch.

4. In a telephone system, calling and called lines, dials associated therewith, a switch for extending a calling line to a called line, a source of signaling current, a relay for disconnecting said source of signaling currentfrom a called line, a second relay and means for releasing said switch controlled by the last-named relay and through contacts of the first-named relay.

5. In a telephone system, a calling line, groups of called lines, a single motion switch for extending said calling line to a line in one of said groups, a stepping magnet, a stepping circuit including said magnet responsive to impulses for controlling the operation of said switch, and means for permanently opening said stepping circuit to prevent further operation of said switch in response to additional impulses from .nc calling line and a circuit for automatically continuing the operation of said switch in case the selected line is busy.

6. In a telephone system, a switch, a line relay therefor, a stepping relay, a circuit for said stepping relay closed upon the operation of said line relay, a motor-magnet for said switch, a circuit therefor controlled by said stepping relay, and a short-circuit for said stepping relay circuit closed through a contact of said line relay for preventing operation of said stepping relay, said short-circuit being independent of said motor magnet, and removed by the release Ill) 

